Do be aware that, because you'll be stopping in the UK for >24 hours rather than just transiting, you will also have to pay the UK APD (departure tax), which will add about another CAD$24 each to your stopover. It's probably insignificant compared to the cost of the trip, but you should be aware of it in case you wonder why the tax on your fare increases by more than you might expect.

There are no *A airlines flying LON-DUB, so AC codeshares with EI. This will mean that you have no advance seat selection, so make sure you get on-line as soon as their check-in opens - you should be able to get seats together, but better to be pro-active rather than wait until the airport. Your baggage allowance should carry over from the AC leg, but make sure you have your confirmation with you in case there's a query - EI is a LCC so will charge for hold luggage. Good news is that they also use T2 at Heathrow, so you'll be familiar with the route back-and-forth.